This invention relates to a polarimeter.
In particular, the invention concerns a polarimeter of the kind which includes a polariser having a fixed orientation and an analyser which is rotatable about its axis. In such a polarimeter the analyser is rotated at constant speed about its axis and the resulting modulation of the light intensity is detected by a light detector arranged to detect the intensity of light transmitted by the analyser. The electrical output signal of the light detector in these circumstances is a Sin.sup.2 waveform of two cycles per revolution of the analyser. When a sample, the optical activity of which is to be measured, is placed between the polariser and the analyser, the phase of the output signal of the light detector is shifted in relation to the angular position of the analyser by an amount which is proportional to the optical rotation introduced by the sample. Measurement of this phase shift in the output signal of the detector thus gives a measure of the optical activity of the sample.
Known polarimeters of this kind have employed electrical signals of sinusoidal waveform to control a motor driving the analyser and have used analogue methods of determining the phase shift in the output signal of the light detector. Efforts to improve such known polarisers have concentrated on attempts to improve the synchronism of the rotation of the analyser in relation to the controlling waveforms and attempts to obviate the inherent drawbacks in the analogue phase shift measurement. However, the known polarimeters remain relatively inaccurate.
It is an object of the present invention to provide an improved polarimeter using digital techniques.